Electrostatic compositions comprising sodium salt of mahogany sulfonic acid, polar solvents and water



United States Patent This invention concerns novel electrostatic conductivity additives and compositions containing them. Specifically, it pertains to additives consisting of oil-soluble sulfonates, water and polar solvents which are used in electrostatic coating compositions.

A substantial portion of industrial paints are now applied electrostatically. This method of application con sists of utilizing a high-voltage, low-current mechanism to atomize and charge the coating compositions. The spray particles of the coating compositions carry a negative charge, whereas the object to be coated is positively charged and grounded. Consequently, the particles are attracted to the object, where they adhere and lose their charge. This method of application results in the entire article being evenly coated, thereby yielding increased coverage per gallon of coating composition. Other advantages of this method of application are that it eliminates loss of coating composition from overspray, reduces labor requirements, and reduces air pollution. Wooden workpieces containing more than approximately moisture may be grounded in the same fashion as metal objects and may be sprayed electrostatically.

Since this unique application requires that the coating I particles be electrically charged, electrical conductivity is an essential property of the coating material. Moreover, the coating material must have electrical conductivity within a certain range to facilitate proper coating. This range varies with the type of coating material. Most coating compositions do not inherently possess this required degree of electrical conductivity. Therefore, substances which impart electrical conductivity must be added to the coating. Presently, coating compositions contain as much as 30% expensive polar solvent additives such as methylethyl ketone, methanol and nitromethane in order to increase their conductivity to an acceptable level.

The novel electrostatic conductivity additives of the invention comprise oil-soluble sulfonates, water and polar solvent. Although the addition of either polar solvents or mixtures of oil-soluble sulfonates plus water to base coating compositions would alone increase their conductivities, it has been found that additive compositions containing all three of the aforementioned substances remarkably increase conductivities of coating compositions. In addition, it has been determined that the weight ratio of water to oil-soluble sulfonate is critical to the stability of these compositions. Mixtures having water to sulfonate weight ratios of from about 0.3 to about 2.0, that is, 0.3:1 to 2.0:1, do not separate into distinct phases at normal temperatures and are more effective than other mixtures. Thus, compositions having such water to sulfonate ratios are more easily handled and blended with base coating compositions. For this reason a preferred embodiment of the invention is compositions comprising oil-soluble sulfonates, water and polar solvents having water to oil-soluble sulfonate ratios of the above-described range. Particularly preferred are compositions consisting essentially of from about 30 to 70 weight percent oil-soluble sulfonate, from about 20 to weight percent water, and from about 5 to 50 weight percent polar solvent.

Generally the sulfonate proportion of the novel additives can consist of any oil-soluble sulfonate. However, sulfonates selected from the group consisting of alkali, alkali earth, and amine salts of oil-soluble sulfonates are preferred. Particularly preferred is sodium mahogany sulfonate.

Any typical organic solvents which have polar characteristics may be used in the additive composition. Examples of these solvents are esters, amides, ketones, alcohols, nitroaromatics, and nitroparafiins. Particularly suitable are polar solvents selected from the group consisting of alkyl ketones, alkyl alcohols, and nitroparatilns. Preferred species of these three classes are alkyl ketones having from 1 to 8 carbon atoms, alkyl alcohols having from 1 to 8 carbon atoms and nitroparaffins having from 1 to 4 carbon atoms. Methanol, methylethyl ketone and nitromethane are particularly preferred because of their excellent polar qualities and commercial availability.

Due to their remarkable conductivity enhancing qualities, only small amounts of the new additives are required to adjust the conductivities of coating compositions to levels acceptable for electrostatic application. Consequently, these novel conductivity additives greatly reduce the amount of conventional polar solvent necessary to adjust conductivity. Either all or the bulk of the expensive polar solvents presently used may be replaced by inexpensive hydrocarbon solvents which may be chosen based on their volatility and solvent power rather than their conductivity inducing properties.

The great majority of industrial coating compositions electrostatically applied are baking enamels which have some initial conductivity. It has been found that the conductivity of these enamels may be adjusted to optimum value for electrostatic application by the addition of less than 1% of the new additives. Other industrial coating compositions such as air-drying enamels, which have essentially no initial conductivity, may require the addition of about 3% of the new additive with a few percent conventional polar solvent to bring their conductivity to a satisfactory level. However, the amount of conventional polar solvent necessary to adjust conductivity is always much less than would be required without the addition of the new additives of the invention. Neither the viscosities nor other properties of coating compositions are disturbed by the addition of the new additives. In addition, the new "additives present storage advantages j (less volume) and eliminate the odor problems'involved in using conventional polar solvents.

Table I contains various additive compositions and is a tabulation of the additives tested in the following Table Table 11 illustrates the comparison between the amounts of a commonly used polar solvent, methylethyl ketone, and amounts of various new additive composition required to achieve a Ransburg resistance of 0.2 megohms in coating compositions. Since Ransburg resistance is inversely related to conductivity, .the former may be used to determine the acceptability of coating materials for electrostatic application. In fact, Ransburg resistance as determined with a Ransburg resistance meter is the commonly used measure of acceptability for electrostatic application. This meter is essentially an ohmmeter adapted to measure the electrical resistance through a fixed'volume of coating composition. On the Ransburg resistance scale one megohm represents megohmcm. of specific resistivity. The desirable coating-resistance range recommended by Ransburg for electrostatic application is 0.1 to 1.0 megohrns. However, the optimum resistance may vary with the individual coating compositions and their end uses.

TABLEI stituent. classified according to their binder component.

Additive Composition (weight percent) components such as drying agents, antiskinning agents, Designawetting agents, and the like may be incorporated into the tion Sultomtc Polar Solvent Water coating compositions depending upon the desired end v properties. A gig l g a gg b ketmer 0 Coating compositions susceptible to electrostatic ep- 13 Calciuni mahogany sul- Methylethyl ketone, 33. 3 plication are those whose viscosity can be adjusted to C ffflfiff f'i ,,Z2;, 33,3 p y consistency These coatings ipclude those based D Ethylene diamire dode- Methylethyl ketone, 33. 3 on oleoresrnous varnishes, alkyd 1'6S1l1S, amino resins, ga sulfonate phenolic resins, chlorinated rubber resins, rubber resins, E do wthal rol, 33.3. 23.3 acrylic ester resins, cellulosic resins, vinyl resins and F gifgg gg b? 1 3 smmty 9 waxes. These coating compositions combined with oil- Mgghoylisoamyl ketone, 25. 0 soluble sulfonates, water and polar solvents constitute Diis'obutyl ketone, 250" 0 novel electrostatic coating compositions. A variety of Nitropropans. means can be employed to incorporate these substances Amyl alcohol, 25.0 2o. 0 Methylamyl alcohol, 250 into the base composition. Stable mixtures of oil-soluble 25.0. sulfonates plus water having weight ratios of water to sulfonate of from about 0.3 to 2.0 can be added followed TABLE II Volume percent of conductivity additive required in Base coating composition (weight percent) various coating corn positions to achieve Ransburg No. Drying resistance of 0.2 megohms method Methyl- Desig- Plgment Blnder Volatile solvent; Misc. ethyl nation Additive ketone 1 Titanium oxide, 26.8...--. Soya alkyd resin, 50.3; Isopropyl alcohol, 3.9; 0. 2 Bake.... 4. 4 A 0.0

melamine formaldehyde xylene, 4.9. resin, 13.9. 2 Titanium oxide, 4.0; alu- Dehydrated castor alkyd Aromatic hydrocarbons 0.1 ...do..--. 7. 4 A 0.0

rninum stearate, 0.2; resin, 40.0; urea for- B.R. 360-400 F., 6.0; lemon yellow oxide, 7.2; nmldehyde resin, 20.2. denatured alcohol, 3.4; chrome green medium, xylene, 4.9. 0.7; lamp black, 0.4. 3 Titanium oxide, 26.7 Styrenated alkyd resni, Xylene, 3.7; n-butanol, 0.4 .-do..... 1.5 A 0.15

48.5; melamine iormal- 13.7. dchyde resin, 17.0. 4 Titanium oxide, 24.6.".-. Dehydrated caster alkyd Xylene, 3.5; n-butanol, 0.4 ..-do 3.4 A 0.0

rosin, 44.3; melamine 3.5. formaldehyde resin, 23.7. 5 Titanium oxide, 31.9; Styrenated alkyd resin, Xylene, 3.2 1. 8 Air-dry. 17. 0 A

zinc oxide, 2.3. 01.0. I 6 Titanium oxide, 29.0 Soya. alkyd resin, 46.4"... Aromatic hydrocarbons 1. 4 ..-do..-.. 29. 0 A

B.R. %0330 F., 23.2. Long oil alkyd resin, 30.0-- Aromatic hydrocarbon 0.0 30, 0 B 4, 4

B.R. 280-330 F., 70.0. 4) do do 00 30.0 G 3.4 do 0.0 30.0 D 5.9 4 do dn 0.0 30. 0 E 5.2 Titanium oxide, 4.0; alu- Dehydrated castor alkyd Aromatic hydrocarbon 0.1 Bake.... 7. 4 F 1. 2

minum stcarate, 0.2; resin, 40.0; urea formal- B.R. 360-400 F., 6.9; lemon yellow oxide, 7.2; dchyde resin, 20.0. denatured alcohol, 3.4; chrome green medium, xylene. 4.0. 0.7; lamp black, 0.4. do 0.1 .do 7.4 1.4 0.1 .do. 7.4 1.4 0.1 ...do... 7.4 1.0 0.1 .do. 7.4 1.4 0.1 ..do 7. 4 1. 5

1 B.R.=Boiling range.

3 4%+3% methanol.

4 Pigments, which display no effect upon conductivity, were onntted.

Basically, coating compositions consist of pigments, volatile solvents and organic binders. Pigments are finely powedered materials which are practically insoluble in the binder. The type of pigment used depends upon the color, opacity and filling properties desired to be imparted to the coating composition. The volatile solvent is used to reduce the coating composition viscosity to a level at which the composition can be satisfactorily applied. Volatile solvents include a variety of organic liquids whose use varies with their commercial availability and tht solubility characteristics of the particular binder being employed in the composition. Examples of some commonly used volatile solvents are mineral spirits, toluene, n-butanol, xylenes, etc. The binder is an organic material, usually a resin or oil, which binds the pigment particles into a coherent film and provides the necessary adhesion of that film to the surface on which it is applied. The end use of the coating composition is primarily dependent upon the nature of the binder conby the addition of an amount of polar solvent necessary to obtain a desirable conductivity level.

The following examples illustrate the effectiveness of this particular method.

Example I A coating composition containing 800 g. titanium oxide, 1280 g. medium oil alkyd resin, 1540 g. aromatic hydrocarbons having a boiling range from 280 to 330 F., 16 g. calcium naphthenate, 8 g. cobalt naphthenate, 19 g. lead naphthenate land 4 g. antiskinning agent was compounded. To approximately 290 ml. of this composition 1.3 ml. of a 1:1 solution by weight of water to sodium mahogany sulfonate was added. The Ransburg resistance of this mixture was adjusted to 1.1 megohms by the addition of 25.0 ml. methylethyl ketone. When methylethyl ketone alone is added 123 ml. of the ketone is required to adjust the Ransburg resistance to 1.1 megohms.

r Example II A base coating composition containing 800 g. titanium oxide, 1280 g. medium oil alkyd resin, 1240 g. aromatic hydrocarbons having a boiling nange from 280 to 6 of evaluating coating performance. One such testing method consists of spraying coating compositions with the Ransburg electrostatic hand spray gun fixed six inches from a grounded metal sheet and evaluating the result- 3300 PU 16 g calcium naphthmate, 8 g. cobalt naph 5 ing spray patterns. A satisfactory spray pattern should thenate, and 4 g. antiskinning agent was compounded. be a Sharp doughnut having a diamdm' of To approximately 290 ml. of this composition 0.9 ml. from 15 2O i n .Small Vold spot m l of a 1:1 Solution by Weight of Water to sodium mahog ter. There shotud be a minimum of droplet scattering any sulfonate was added The Rvansburg Tesistance of and fine EILOITllZfltlOIl should be apparent at the outer edge this was adjusted to 1.1 megohms by the addition of 15.0 of the ma Spray patterns l .urea a k resm m1. methannl. Approximately 19 m1. of methanol by enamels containing the new conductivity additives were self is required to adjust the resistance or" 290 ml. of this of fine coating composition tol lmegohms The durability of the coating film is one of its most important properties. Electrostatic spraying is simply Example III an application technique, and any constituent added to To 290 ml. of the base coating composition of Example lmpmvfe conduqtivity Should no on ma inherent II, 0.9 ml. of a 1.1 solution by weight of water to sodium protect! e qualmes of the @R coatmg' The date in mahogany sulfonate was added The Ransburg resist Table III show that the additives of the present invention ance of this mixture was adjusted to 1'1 megohms by the have no detrimental effect on weatherability, adhesion, addition of 24.0 ml. of nitromethane. Approximately 20 or hardness of the Coatmg films formed by thfi test 36 m1. of nitromethane by itself is required to adjust the f' resistance of 290 ml. of this coating composition to 1.1 weathgablhty of the cpatmg films was determined megohms' by exposmg them to ultraviolet radiation and moisture at A prefarred method is to directly incorporate Com room temperature in an Atlas Weather-Ometer for 144 ductivity additive compositions comprising all three subholurs and measuring ths Change m gloss at 164mm inter stances. Such a method Was used to obtain most of the Va data contained in Table II Either method results in novel Hardness measured 311th the Sward hardness rocker cling to t e method escribed in the Paint Testing coating compositions comprising a major proportion of a accor base coating composition of sprayable viscosity and a Manual 12th Edition 1962 by i and minor proportion of from about 0.1 to 2.0 volume perswam page Vilma Shawn m T In is the cent oil-soluble sulfonate, from about 0.03 to 2.0 volume number of Swmgs mumphed by The higher the percent water and from about 0.03 to 10 volume the {larder the percent polar solvent. The expressed volume percentages P was. determmiid by at} adheslve tape method are based upon the total coating composition. The pre- F also m the 9? Testmg M ferred method results preferably in novel coating com- The {method mv01ves scnbmg cross 1n the Palm positions comprising a major proportion of base coating applymg Piece of f Over the cross and Pulling the composition and a minor proportion suflicient to enhance tape 0m The adheslon is rated on a Scale fmm 1 to the electrical conductivity of the composition of the condepending p tho amount of the Paint that is removed ductivity additive consisting essentially of from about With the ta e. The highest number indicates the best 40 p :0 to 70 weight percent oil-soluble sulfonate, from about adhesion.

TABLE III Gardner gloss 1 Adhesion rating 2 Swat-d hardness 3 Coating composition 5 Before After Before After Before After weathering weathering 4 weathering Weathering weathering Weathering 93 I 91 2 s 40 so s9 s5 9 9 1s 2s 5+Additivc A. 84 so 2 7 44 2o 2 1 is poor; 10 is goo 3 Highest number is hardest film.

4 144 hours in Weather-Ometer.

5 Coating compositions are those corresponding to Nos. 1-5 in Table II and containing enough of the designated additive to achieve a Ransburg resistance of 0.2 megohm.

20 to Weight percent water and from about 5 to 50 weight percent polar solvent selected from the group consisting of alkyl ketones, alkyl alcohols and nitroparafiins. If the latter method is employed, a preferred range for said minor proportion is from about 0.1 to 4.0 volume percent of the total coating volume.

The ultimate eliectiveness and value of both the additives and the novel coating compositions containing the additives is gauged by the protective and decorative qualities of the new coating compositions. Functional The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

We claim:

1. A novel electrostatic coating conductivity additive composition consisting essentially of from about 30 to 70 weight percent sodium salt of mahogany petroleum sulfonic acid, from about 20 to 65 weight ercent water and testis of coatings is perhaps the most conclusive method from about 5 to 50 weight percent of polar solvent selected from the group consisting of alkyl ketones having from 1 to 8 carbon atoms in the alkyl groups, alkyl alcohols having from 1 to 8 carbon atoms and nitroparafiins having from 1 to 4 carbon atoms, the Weight ratio of said water to said sulfonic acid sodium salt being from about 0.321 to about 2.0:1.

2. The additive composition of claim 1 in which the polar solvent is methylethylketone.

3. The additive composition of claim 1 in which the polar solvent is nitromethane.

4. The additive composition of claim 1 in which the polar solvent is methanol.

5. A novel electrostatic coating composition comprising a base coating composition of sprayable viscosity and 6. The coating composition of claim 5 in which the polar solvent is methylethylketone.

References Cited by the Examiner UNITED STATES PATENTS 2,419,048 4/1947 Althouse 26029.2 2,723,921 11/1955 Starkey 1l7 93.4 3,112,218 11/1963 Spiller 11793.4

OTHER REFERENCES from about 0.1 to 4.0 volume percent of the additive com- 15 SAMUEL H. BLECH, Primary Examiner.

position of claim 1. 

1. A NOVEL ELECTROSTATIC COATING CONDUCTIVITY ADDITIVE COMPOSITION CONSISTING ESSENTIALLY OF FROM ABOUT 30 TO 70 WEIGHT PERCENT SODIUM SALT OF MAHOGANY PETROLEUM SULFONIC ACID, FROM ABOUT 20 TO 65 WEIGHT PERCENT WATER AND FROM ABOUT 5 TO 50 WEIGHT PERCENT OF POLAR SOLVENT SELECTED FROM THE GROUP CONSISTING OF ALKYL KETONES HAVING FROM 1 TO 8 CABON ATOMS IN THE ALKYL GROUPS, ALKYL ALCOHOLS HAVING FROM 1 TO 8 CARBON ATOMS AND NITROPARAFFINS HAVING FROM 1 TO 4 CARBON ATOMS, THE WEIGHT RATIO OF SAID WATER TO SAID SULFONIC ACID SODIUM SALT BEING FROM ABOUT 0.3:1 TO ABOUT 2.0:1. 